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CHEM 111 (69)
Lecture

Brief history of the atom, cathode rays, gold foil experiment, basic atomic structure, atomic abbreviations

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Department
Chemistry
Course
CHEM 111
Professor
Dana Johnson
Semester
Fall

Description
30 August Try to solve. If a raindrop weighs 0.52 mg on average and 5.1 x 10 raindrops fall on a lawn every minute, what mass (in kg) of rain falls on the lawn in 1.5 hours? Brief history of the atom Element – simplest type of matter that retains its physical and chemical properties, consists of only 1 type of atom Democritus (c. 460 – 370 BC) – proposed the existence of the smallest particle of a substance, called ‘atoms’ from atomos (Gr. “uncuttable”) John Dalton (1766 – 1844) – proposed modern picture of the atom, still considered to be indivisible, each element has unique atoms Cathode rays J. J. Thomson (1856 – 1940) – worked with cathode rays (electric current) to determine their mass, calculated to be 1 / 1000 that of a hydrogen atom →there must be something smaller than an atom “Plum pudding model” resulted Gold foil experiment Ernest Rutherford (1871 – 1937) – demonstrated that the atom was mostly empty space and the existence of a small, positively charged nucleus with most of the mass Basic atomic structure Shape – spherical with a small, positive nucleus surrounded by one or more negative electrons Nucleus Takes up most of the mass (~99.97% of the total) but takes up only a quadrillionth of the volume (1 x 10 )15 Consists of protons and neutrons (hydrogen the exception)
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